In engine fuel delivery systems of current design, fuel is typically fed by a constant-delivery pump from a fuel tank to the engine. A pressure regulator maintains constant fuel pressure at the engine, and excess fuel is returned from the engine to the fuel tank. Such return fuel carries engine heat to the fuel supply tank, and consequently increases temperature and vapor pressure in the fuel tank. Venting of excess vapor pressure to the atmosphere not only causes pollution problems, but also deleteriously affects fuel mileage. Excess fuel tank temperature can also cause vapor lock at the pump, particularly where fuel level is relatively low. Constant pump operation also increases energy consumption, while decreasing both fuel pump life and fuel filter life. It is therefore desirable not only to eliminate the necessity for the fuel return line from the engine to the supply tank (while still maintaining constant fuel pressure at the engine), but also to control pump operation as a function of fuel requirements at the engine both to maintain constant fuel pressure at the engine and to increase pump life.
U.S. Pat. No. 4,728,264 discloses a fuel delivery system in which a d.c. motor fuel pump delivers fuel under pressure from a supply tank to an engine. A pressure-sensitive switch, which may be contained within a unitary pump/motor housing, is responsive to fuel pump output pressure for applying a pulse width modulated d.c. signal to the pump motor, and thereby controlling pump operation so as to maintain constant pressure in the fuel delivery line to the engine independently of fuel demand. U.S. Pat. No. 4,789,308 discloses a self-contained fuel pump that includes an electronic sensor in the pump outlet end cap responsive to fuel outlet pressure for modulating application of current to the pump motor and maintaining a constant pressure in the fuel delivery line to the engine. Copending U.S. application Ser. No. 07/324,649 filed Mar. 17, 1989, now U.S. Pat. No. 4,926,829, discloses a fuel delivery system in which a pressure sensor is coupled to the return line from the engine for detecting return flow of excess fuel to the supply tank. The output of a pulse width modulation amplifier to the fuel pump motor is controlled as function of the signal from the pressure sensor. The noted patents and application are all assigned to the assignee hereof.
Although the fuel delivery systems disclosed in the noted patents and application address and overcome a number of problems theretofore extant in the art, further improvements remain desirable. For example, it is desirable to provide a fuel delivery system that can be employed in conjunction with fuels of differing alcohol concentrations without requiring service or operator adjustment. Potential for energy release (BTU/unit volume) for gasoline is much greater than for alcohol. For this reason, a quantity of fuel having 90% alcohol concentration delivered to the engine cylinders, for example, must be increased 50% as compared with straight gasoline to maintain constant throttle response and other engine operating characteristics. It has heretofore been proposed to accommodate increased fuel delivery by increasing injector activator time. However, the range of times necessary to accommodate all projected gasoline/alcohol mixtures exceeds the dynamic range of current injector technology.
It is therefore a general object of the present invention to provide a fuel delivery system for internal combustion engines that automatically tailors fuel delivery to fuel alcohol concentration and type (either ethanol or methanol) without operator or service intervention. Another object of the present invention is to provide a fuel delivery system of the described character in which the fuel return line from the engine to the supply is eliminated, thereby reducing the problems of vapor generation and the like previously noted, and in which fuel delivery is maintained at constant pressure (for a given fuel alcohol concentration) by selectively controlling pump operation. It is yet another object of the present invention to provide a self-contained electric-motor fuel pump for use in systems of the described character that features an economical and reliable pump package assembly.